My first answer: everything.
My full answer: the characters are great, especially the main 4. I find Shaxs and T'Ana a little one note - though they both have their good bits and I like Shaxs better. I love how passionate they all are about their jobs and Starfleet. I like the continued showing of how Starfleet is good (though per McMahan: they can always do better) as opposed to how some of DIS and PIC show Starfleet. I like the pacing: with only ~22 minutes you got to get everything in you can to feel like a whole episode (PRO episodes always feel only like half a story cause they don't really move like LDS). I find the show often very funny, if not continuously uproarious; I tend to laugh out loud often and in most episodes. I enjoy the references to past Trek and don't mind the "memberberries" aspect of them, because for the most part they are just fun additions and not essential to the plotlines or something the whole show hinges upon (which would get boring). I like that the characters are learning and growing. I like the visuals; it wasn't my preferred animation style when it started, but I have grown to like it and it is always beautiful. But most of all, I think I like the heart that they put into most every episode. Just when you think they are just going to go some standard "sitcom" plot point they throw the heart in the episode: in this one it was the security guards really appreciating ensigns enjoying their job and then again with Freeman's salvation being Starfleet working as it should and doing it in the background as a pure Lower Decks move. The suprising heart moment that I remember most in the series is probably when Rutherford says he wants to switch back from Security to Engineering and, instead of getting mad, Shaxs and the rest of security division cheer him on for choosing to be himself.